This application claims the benefit of Korean Application No. 00-14550, filed Mar. 22, 2000, in the Korean Patent Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an error signal detecting apparatus for an optical recording/reproducing apparatus, and more particularly, to an error signal detecting apparatus for an optical recording/reproducing apparatus which can detect a relative tangential tilt error signal between an objective lens and a recording medium by using a main beam to record/reproduce information signals on/from a recording medium.
2. Description of the Related Art
In general, an optical pickup records and reproduces information signals while moving across a recording medium such as a disc rotating on a turntable. When the rotating disc is tilted due to a warp in the disc or an error in installation of the disc, the recording and reproducing signals deteriorate.
In particular, in the case of an optical pickup adopting a light source for emitting light having a short wavelength and an objective lens having a large numerical aperture (N.A.) to increase the density of recording, since an optical aberration is proportional to xcex/(NA)3, a large coma due to the tilt of a disc is generated so that recording and reproducing signals are further deteriorated.
Thus, to prevent the deterioration of the recoding/reproducing signals by detecting the amount of the tilt of the disc to compensate for the tilt, a conventional apparatus 100 for detecting a relative tilt between a disc 10 and an objective lens 7 by using a detection signal of a photodetector 9 for reproducing is known, as shown in FIG. 1.
Referring to FIG. 1, laser light emitted from a light source 1 for recording and reproducing information signals passes through a beam splitter 5 and is then input to the objective lens 7. The objective lens 7 focuses incident light emitted from the light source 1 to form an optical spot on a recording surface of the disc 10. Light reflected by the recording surface of the disc 10 passes through the objective lens 7 and is reflected by the beam splitter 5 to proceed toward the photodetector 9. Here, reference numeral 8 denotes a photosensing lens for focusing the incident light reflected by the beam splitter 5 and detected by the photodetector 9.
The photodetector 9 is formed of four separate plates A, B, C and D, as shown in FIG. 2, each independently performing a photoelectric conversion with respect to the incident light thereof. Thus, information and error signals are detected by appropriately adding and/or differentiating detection signals generated by the respective separate plates A, B, C and D.
Referring to FIG. 2, the conventional tilt error signal detecting apparatus 100 includes the photodetector 9 for reproducing information signals. The photodetector 9 is formed of four separate plates A, B, C and D, first and second adders 11 and 13 for respectively adding the detection signals of the separate plates A and B and the separate plates C and D, and a differentiator 15 for subtracting the signals input from the first and second adders 11 and 13 to output a tangential push-pull signal as a tilt error signal.
The tilt error signal output from the conventional tilt error signal detecting apparatus 100 having the above structure is input to an apparatus for adjusting the relative tilt between the objective lens 7 and the disc 10, to thereby correct the tangential tilt error.
Since the conventional tilt error signal detecting apparatus 100, although it has the advantage of a simple structure, detects the tangential tilt error signal by subtracting the detection signals of the separate plates at either side with respect to a center axis of the photodetector 9 which is parallel to the radial direction of the disc 10, when the objective lens 7 is shifted or the distance between the objective lens 7 and the disc 10 is deviated from an on-focus position, the signal output therefrom changes, and thus the tangential tilt error cannot be accurately detected.
Also, the profile of a light beam, which is focused on the disc 10 as an optical spot and is reflected/diffracted, as shown in FIG. 3, and is detected by the photodetector 9 according to the tangential tilt between the objective lens 7 and the disc 10, changes. This is shown in FIGS. 4A though 4C. Thus, the conventional tilt error signal detecting apparatus 100 as described with reference to FIGS. 1 and 2 cannot accurately detect the tangential tilt error signal.
FIG. 3 shows the light reflected by the disc 10 in a land/groove format and diffracted to the 0th order and the xc2x11st order. As shown in FIG. 3, the 0th order and the xc2x11st order diffraction light overlap one another in a radial direction of the disc 10. Also, some areas of the +1st order diffraction light and the xe2x88x921st order diffraction light may overlap one another.
FIGS. 4A through 4C show the profiles of a light beam reflected by the disc 10 in land/groove format such as next generation DVDs, and so-called HD-DVD RAM discs, in which a track pitch is, for example, 0.37 xcexcm and is detected by the photodetector 9. FIG. 4A shows the case in which a negative tangential tilt error of about xe2x88x920.5 degrees occurs. FIG. 4B shows the case in which the tangential tilt error does not occur. FIG. 4C shows the case in which a positive tangential tilt error of about +0.5 degrees occurs.
As can be seen from FIGS. 4A and 4C, when the tangential tilts are generated in opposite directions, light beams landing on the separate plates A and D and the separate plates B and C show patterns of the profiles of the light beams opposing each other with respect to a center axis in the tangential direction. Also, the beam profile mainly lands on the inner portion of the separate plate with respect to the tangential tilt in one direction, and on the outer portion of the separate plate with respect to the tangential tilt in the opposite direction.
As described above, in the conventional tilt error detecting apparatus using the photodetector 9 having four separate plates, a tangential tilt error signal is detected by subtracting a sum signal of the detection signals of the separate plates C and D from a sum signal of the detection signals of the separate plates A and B. Therefore, the conventional tilt error detecting apparatus is not able to accurately detect a change in the beam profile according to the tangential tilt and thus an accurate tangential tilt error signal cannot be detected.
Accordingly, it is an object of the present invention to provide an error signal detecting apparatus for an optical recording/reproducing apparatus which can detect a change in the profile of a light beam according to the tangential tilt by adopting a photodetector so that a highly accurate tangential tilt error signal can be detected.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and, in part, will be obvious from the description, or may learned by practice of the invention.
The foregoing and other objects of the present invention are achieved by providing an error signal detecting apparatus for an optical recording/reproducing apparatus comprising a photodetector to receive [for receiving] light reflected and diffracted by a recording medium, and a signal processor to detect an error signal by calculating a detection signal of the photodetector, in which the photodetector includes a plurality of light receiving areas, each independently receiving light where the profile of a beam changes to the opposite profile according to the tangential tilt of the recording medium, and the signal processor detects a tangential tilt error signal from detection signals of the light receiving areas.
It is preferred in the present invention that the photodetector has at least six separate structures and comprises first and second inner light receiving areas arranged in a tangential direction of a track of the recording medium, first and second outer light receiving areas arranged at both sides of the first inner light receiving area in a radial direction of the recording medium, and third and fourth outer light receiving areas arranged at one side of the second and first outer light receiving areas, and at both sides of the second inner light receiving area, in the radial direction of the recording medium. The signal processor comprises a first adder to add a detection signal of the first inner light receiving area and detection signals of the third and fourth outer light receiving areas, a second adder to add a detection signal of the second inner light receiving area and detection signals of the first and second outer light receiving areas, and a differentiator to subtract the detection signals received from the first and second adders and to output a tangential tilt error signal.
In another embodiment of the present invention, when light reflected/diffracted by the recording medium is divided into a pair of inner and outer light areas on the radial direction of the recording medium, the photodetector includes first and second inner light receiving areas arranged along the tangential direction of the track of the recording medium, each independently performing photoelectric conversion by receiving light of the inner light area. Furthermore, the signal processor comprises a differentiator to receive and subtract the detection signal of the first inner light receiving area and the detection signal of the second inner light receiving area, and output the tangential tilt error signal.
In another embodiment of the present invention, when light reflected/diffracted by the recording medium is divided into a pair of inner and outer light areas in the radial direction of the recording medium, the photodetector includes first and second outer light receiving areas arranged along the tangential direction of the track of the recording medium, each independently performing photoelectric conversion by receiving light of part of the first and second outer light areas, and third and fourth outer light receiving areas arranged at one side of the second and first outer light areas in the tangential direction of the recording medium, each independently performing photoelectric conversion by receiving the other part of the outer light area, in which the signal processor outputs a differential value between a sum signal of the detection signals of the first and second outer light receiving areas and a sum signal of the detection signals of the third and fourth outer light receiving areas as the tangential tilt error signal.
In another embodiment of [in] the present invention, the photodetector comprises first and second inner light receiving areas arranged in the tangential direction of the track of the recording medium, first and second outer light receiving areas arranged at both sides of the first inner light receiving area in the radial direction of the recording medium, and third and fourth outer light receiving areas respectively arranged at one side of the second and first outer light receiving areas at both sides of the second inner light receiving area in the radial direction of the recording medium, and has at least six separate structures, in which the signal processor comprises a first differentiator to receive and subtract the detection signal of the first inner light receiving area and the detection signal of the second inner light receiving area, a second differentiator to receive and subtract a sum signal of the detection signals of the first and second outer light receiving areas and a sum signal of the detection signals of the third and fourth outer light receiving areas, and an adder to add output from the first and second differentiators and output a tangential tilt error signal.
According to an aspect of the present invention, the recording medium is in a land/groove format, and the tangential tilt error signal output from the signal processor exhibits the opposite polarity of a land/groove.
According to another aspect of the present invention, the signal processor further comprises an inverter to selectively invert and output the polarity of the detected tangential tilt error signal according to a land/groove determination value of a system controller, to determine a land or a groove.